Known from the prior art are methods for leaching a sulfidic metal concentrate in a leaching process in hydrometallurgical production of metal. Hot water vapor containing off-gas is conducted out from the leaching process. On the other hand, an acid solution warmed up to an elevated temperature is conducted to the process. Such methods are known for example from patent publications FI100806B, WO 2004/076698A1 and articles “Outotec Direct Leaching application in China”, Haakana T., Saxén B., Lehtinen L., Takala H., Lahtinen M., Svens K., Ruonala M, Xiao ming; Lead & Zinc 2008, International Symposium on Lead and Zinc Processing, Durbaan, South Africa, 25-29 Feb. 2008, and “Zinc Plant Expansion by Outotec Direct Leaching Process”, M. Lahtinen, K. Svens, T. Haakana, L. Lehtinen, Zinc and Lead Metallurgy, L. Centomo, M. J. Collins, J. Harlamovs, and J. Liu, Eds., Canadian Institute of Mining, Metallurgy and Petroleum (COM2008), Winnipeg, Canada 2008, 167-178, describing the direct leaching of zinc. Further known from publication FI 121713 B is a copper leaching method. A nickel leaching method is known from publication FI 121180 B relating to the leaching of nickel laterite ores.
In the leaching of a sulfidic metal concentrate, the sulfide leaching process produces exothermic reactions, generating a considerable amount of heat. This heat is removed from the leaching step in a hot water vapor containing off-gas. The off-gases carry out considerable amounts of energy in the form of water vapor of approximately 100° C. Normally, the off-gases are conducted to the atmosphere through a gas scrubber. On the other hand, an acid solution to be fed to the leaching process is warmed up with vapor produced by oil, natural gas or other such external heating energy source, producing great equipment investment costs, energy costs for the external heating energy and carbon dioxide emissions.